Hereinafter, a general MIMO system and a collaborative MIMO system will be briefly described.
Recently, the MIMO system has come into the spotlight as a wideband wireless mobile communication technology. In particular, the MIMO system can improve spectrum efficiency in proportion to the number of antennas, which is hard to be realized in the existing single input single output (SISO) communication technology.
The MIMO technology refers to a multi-antenna technology of realizing high-speed communication using multiple antennas. The MIMO technology may be divided into a spatial multiplexing scheme and a space diversity scheme depending on whether or not the same data is transmitted.
The spatial multiplexing scheme refers to a scheme of simultaneously transmitting different data via several transmission/reception antennas. That is, a transmitter transmits different data via transmission antennas and a receiver receives the transmitted data by performing suitable interference elimination and signal processing, thereby improving a transfer rate by the number of transmission antennas.
The spatial diversity scheme refers to a scheme of transmitting the same data via multiple transmission antennas and obtaining transmission diversity. That is, the spatial diversity scheme is a space-time channel coding scheme. The spatial diversity scheme can maximize a transmission diversity gain (performance again) by transmitting the same data via the multiple transmission antennas. The spatial diversity scheme can improve transmission reliability due to the diversity gain, but cannot improve the transfer rate.
In addition, the MIMO technology may be divided into an open loop scheme (e.g., a Bell Labs layered space time (BLAST), a space time trellis code (STTC) or the like) and a closed loop scheme (e.g., transmit adaptive array (TxAA) or the like) depending on whether channel information is fed back from the receiver to the transmitter.
The collaborative MIMO is suggested in order to reduce inter-cell interference in a multi-cell environment. If the collaborative MIMO system is used, a mobile station may commonly receive data from multi-cell base stations. In addition, the base stations can simultaneously support one or more mobile stations MS1, MS2, . . . , and MSK using the same radio frequency resource in order to improve system performance. In addition, each of the base stations can perform a space division multiple access (SDMA) method on the basis of channel state information between the base station and the mobile station.
In the collaborative MIMO, a serving base station and one or more collaborative base stations are connected to a scheduler via a backbone network. The scheduler may receive channel information representing the channel state between the mobile stations MS1, M2, . . . , and MSK and the collaborative base stations, which is measured by the base stations BS1, BS2, . . . , and BSK via the backbone network, and may operate on the basis of the channel information. For example, the scheduler schedules information for a collaborative MIMO operation with respect to the serving base station and one or more collaborative base stations. That is, the scheduler directly instructs the base stations to perform the collaborative MIMO operation.